Japan took a historic step away from its post-war pacifism on Tuesday by ending a ban that has kept the military from fighting abroad since 1945, a victory for Prime Minister Shinzo Abe but a move that has riled China and worries many Japanese voters.

The change, the most dramatic shift in policy since Japan set up its post-war armed forces 60 years ago, will widen Japan's military options by ending the ban on exercising "collective self-defence," or aiding a friendly country under attack.

Long constrained by the post-war constitution, Japan's armed forces will become more aligned with the militaries of other advanced nations in terms of its options. However, the government will be wary of putting boots on the ground in multilateral operations such as the 2003 U.S.-led invasion of Iraq.

Abe repeated that stance on Tuesday, while stressing Japan had to respond to an increasingly tough security environment.

'Cannot send troops overseas'

"There is no change in the general principle that we cannot send troops overseas," Abe told a televised news conference, flanked by a poster showing Japanese mothers and infants fleeing a theoretical combat zone on a U.S. vessel under attack.

Japan's Prime Minister Shinzo Abe has pushed to end a ban that has kept the military from fighting abroad since World War Two. (Issei Kato/Reuters)

The United States, which defeated Japan in the Second World War then became its close ally with a security co-operation treaty, welcomed the Japanese move.

"We have followed with interest the extensive discussion within Japan on the issue of exercising its right under the UN Charter to collective self-defence," State Department spokeswoman Marie Harf told a regular news briefing.

"The U.S.-Japan alliance is one of our most important security partnerships and we value efforts by Japan to strengthen that security co-operation," she said.

However, the new policy has angered an increasingly assertive China, whose ties with Japan have frayed due to a maritime row, mistrust and the legacy of Japan's past military aggression.

"China opposes the Japanese fabricating the China threat to promote its domestic political agenda," Chinese Foreign Ministry spokesman Hong Lei told a news conference in Beijing.

Welcomed by Washington

"We demand that Japan respect the reasonable security concerns of its Asian neighbours and prudently handle the relevant matter."

Abe's advisers have said Tokyo should take no action involving a friendly country without that country's consent.

The shift, however, will be welcomed by Washington, which has long urged Tokyo to become a more equal alliance partner, and by Southeast Asia nations that also have rows with China

Conservatives say the constitution's war-renouncing Article 9 has limited Japan's ability to defend itself and that a changing regional power balance, including a rising China, means policies must be more flexible.

Abe, who took office in 2012 promising to revive Japan's economy and bolster its security posture, has pushed for the change - which revises a longstanding government interpretation of the charter — despite wariness among ordinary Japanese.

Some voters worry about entanglement in foreign wars and others are angry at what they see as a gutting of Article 9 by ignoring formal amendment procedures. The charter has never been revised since it was adopted after Japan's 1945 defeat.

Voters wary

On Sunday, a man set himself on fire near a busy Tokyo intersection — a rare form of protest in Japan — after speaking out against Abe's re-interpretation of Article 9.

While Abe spoke, thousands of protesters, including pensioners, housewives and employees just leaving work, gathered near the premier's office carrying banners and shouting, "Don't destroy Article 9", "We're against war" and "No more Abe".

Legal revisions to implement the change must be approved by parliament and restrictions could be imposed in the process.

Since its 1945 defeat, Japan's military has not engaged in combat. Past governments have stretched the constitution's limits to develop a military now on par with that of France and to permit non-combat missions abroad, but its armed forces remain far more constrained legally than those of other nations.

China has already argued that Japan is raising regional tensions and seeks to back its case by pointing to Abe's efforts to cast Tokyo's wartime past with a less apologetic tone.

"It makes it easier for competitors to paint Japan as a wolf in sheep's clothing," said Richard Samuels, director of the Center for International Studies at the Massachusetts Institute of Technology. But he added: "Just because Japan is strong does not mean that it will be aggressive."